Special purpose telecommunication systems are used to provide a variety of specialized services. One example of such a system is a cellular mobile telecommunication system, which provides the service of connecting mobile telecommunication customers to land-based customers via the common carrier public telephone network. In such a system, all incoming and outgoing calls are funneled through a mobile telecommunication switching office, connected to a group of radio stations which communicate with mobile units. Another example of a special purpose telecommunication system is a private branch exchange complex connected to the common carrier public telephone network and including satellite private branch exchanges connected to a central private branch exchange. In such a system, all incoming and outgoing calls are funneled through the central private branch exchange to customers on the satellite private branch exchanges.
Special purpose telecommunication systems of the type discussed herein are normally characterized by having a two-stage connection process. A first stage is used, for example, to connect the mobile units of a cellular mobile telecommunication system to a communication link leading to the mobile telecommunication switching office or to connect the customers at satellite private branch exchanges to a communication link leading to the central private branch exchange. A second stage, effected in the mobile telecommunication switching office or central private branch exchange, is used to connect the communication link to a telecommunication network such as the common carrier public telephone network. The entire connection process is under the control of processors controlled by a complex program.
One example of a prior art special purpose telecommunication system is the Advanced Mobile Phone Service (AMPS) System described in The Bell System Technical Journal (BSTJ), V. 58, No. 1, Part 3, January 1979, pp. 1-270. In this cellular mobile telecommunication system, the first stage connection is between a mobile unit and a communication link connected to a mobile telecommunication switching office. The mobile units are served by radio stations or cell sites, each of which is located in one cell area of a larger region. Each cell site in the region is connected by a group of communication links to the mobile telecommunication switching office. Each cell site contains a group of radio transceivers (transmitter/receivers), each transceiver being connected to one communication link. Each transceiver operates on a pair of frequencies, one frequency to transmit radio signals to a mobile unit, the other to receive radio signals from the mobile unit. A first-stage connection is set up when a transceiver, operating at a given frequency pair, is turned on and a mobile unit is tuned to the same frequency pair. The second stage of the connection, between a communication link and the common carrier public telephone network, is set up in the mobile telecommunication switching office which is connected to the telephone network by other communication links called incoming and outgoing trunks. The mobile telecommunication switching office contains a switching network to switch a mobile customer speech or a mobile customer data communication from the communication link to an incoming or outgoing trunk.
The mobile telecommunication system is controlled by processors including a mobile telecommunication controller at the mobile telecommunication switching office and a cell site controller at each cell site. A plurality of data links connect the mobile telecommunication controller and the cell site controllers. The mobile telecommunication controller under control of a complex program controls the switching network. It also controls the actions of cell site controllers by generating and interpreting the control messages that are exchanged over the data links. The cell site controllers at each cell site, in response to control messages from the mobile telecommunication controller, control the transceivers at the site. The control processors at each cell site also control the tuning of mobile units.
With today's rapidly moving technology, new and more efficient designs of telecommunication switches and telecommunication control systems are continually being evolved and the demand for new specialized telecommunication services is ever increasing. Prior art telecommunication system designs suffer from inflexibility and are difficult to adapt to the use of new, more cost-effective switching technologies and the offering of new specialized services. For example, to incorporate a new telecommunication switch into an existing specialized telecommunication service system design, or to adapt a prior art system to offer a new kind of telecommunication service, usually requires a major design effort. A complex new telecommunication switch control program must be designed and/or a major redesign of interface hardware between the control system and the units controlled by that system may be required.